Oscillating idle -- 1980 SC
12-03-2005, 11:05 PM
#1
Track Day
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Oscillating idle -- 1980 SC
When started cold, the idle begins as normal, high and smooth fast-idle. After about 15 seconds, it goes into an oscillating mode -- high, low, high, low, .... -- for about 45 seconds (these time depend on the air temp.), then it goes to a smooth idle. I have had it looked at by three, local, Porsche and CIS "experts." They have replaced control-pressure regulator, changed shims in pressure regulator and done a bunch of other things. Nothing changed. One suggested the auxilliary-air regulator was defective. I replaced it with a used one (I could have bought a new engine for the price of a new AAR). Only difference with the replacement AAR was that the idle speed went to about 3000RPM, and I couldn't get it down by adjusting the idle-air bypass screw.
Anyone got any other suggestions for things to check, adjust or replace?
Anyone got any other suggestions for things to check, adjust or replace?
12-04-2005, 11:58 AM
#2
After three "experts" have played with it, your CIS is now probably royaly screwed up. Surging is generally a sign of richness problems. Have you set your CO to the correct setting with a proper gauge? (And no 1/4 turn playing around!) It also looks like your used AAR isn't working properly. With all the help you've gotten, I'd also check the WUR presuures with the proper gauge.
CIS systems are highly adjustable and don't take kindly to random adjustments.
CIS systems are highly adjustable and don't take kindly to random adjustments.
12-04-2005, 02:56 PM
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My 83 SC does exactly the same thing and from what I've read on this forum & others it's very, very common on SC's.
I just live with it now as it's only for the first 20-30 seconds from stone cold!
I just live with it now as it's only for the first 20-30 seconds from stone cold!
12-04-2005, 06:10 PM
#4
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carman: As we move toward winter that cold start surge is entirely OK. It simply means that your cold control pressure is set slightly on the rich side of an acceptable range. The result is protection for the airbox, that light surging gives me great comfort when my '82 does it! It's a shame that your experts spent a lot of your money, a simple adjustment (your car must sit overnight with a pressure gauge installed) can reduce the surge time from 45 seconds to 20-30 seconds, but even that is not necessary. Put your original AAR back on, verify that your CO% is within factory spec, and enjoy the car.
Pete
Pete
